1. Field of the Invention
The present invention relates to an electron-emitting device having an electron-emitting film, an electron source, an image display apparatus, and a method for manufacturing the electron-emitting device.
2. Description of the Related Art
Field emission type (hereinafter, “FE” type) electron-emitting devices are known. Japanese Patent Application Laid-Open Nos. 2004-071536 (US 2006/0066199A1), 8-055564 (U.S. Pat. No. 5,473,218), and 2005-26209 (U.S. Pat. Nos. 7,109,663; 7,259,520) disclose FE type electron-emitting devices having a flat electron-emitting film and a gate electrode with an opening (so-called “gate hole”). In the electron-emitting devices having such a flat electron-emitting film, since a relatively flat equipotential surface is formed on a surface of the electron-emitting film, spread of electron beams becomes small.
The electron-emitting devices used in image display apparatuses require stable electron emission in order to secure reliability such as brightness uniformity of display images. Specifically, ideal properties are such that (1) electron emission characteristics of all the electron-emitting devices are uniform, and (2) an amount of electron emission does not fluctuates over time (that is, no fluctuation of an amount of electron emission is caused).
Like Japanese Patent Application Laid-Open No. 2004-071536 (US 2006/0066199A1), however, an electron-emitting film which contains a lot of metal particles possibly causes a characteristic change (change in electric resistance) due to a heat according to some particle sizes of the metal particles. For this reason, the electric resistance of the individual electron-emitting films changes at a heating step of a manufacturing process, and the electron emission characteristic occasionally varies. Further, when an image display apparatus is driven for a long time, the electric resistance of the electron-emitting film changes due to heat generation of the device itself and an influence of another heating element in the apparatus, and the amount of electron emission might fluctuate. According to studies and considerations by the inventors, as the particle size of the metal particles in the electron-emitting film is smaller, the characteristic change due to such a heat becomes more noticeable. In Japanese Patent Application Laid-Open No. 2004-071536 (US 2006/0066199A1), a carbon film containing a lot of cobalt particles is formed in such a manner that a film which includes cobalt and carbon is formed on a substrate by co-sputtering graphite and cobalt targets, and the cobalt is agglomerated by heating the film at high temperature. Conventionally, complicated steps are occasionally required for forming electron-emitting films containing particles, and preferable control of particle sizes is difficult in some constitutions (materials) of the electron-emitting films.